Referring to FIG. 3, a conventional fuel cell system includes a fuel cell unit 40, a reformer 41, a fuel supply 42, a mixing unit 43, a combustor 44 and a heat exchanger 45. The reformer 41 is connected to the fuel supply 42 through a pipe 421. The reformer 41 is connected to the fuel cell unit 40 through pipes 422 and 423. The mixing unit 43 is connected the fuel cell unit 40 and the reformer 41. The combustor 44 is connected to the mixing unit 43. The heat exchanger 45 is connected to the combustor 44. The heat exchanger 45 includes a fresh air port 451, an exhaust port 452 and a hot air port 453. The heat exchanger 45 is connected to the fuel cell unit 40 through the hot air port 453. In use, fuel is sent into the reformer 41 from the fuel supply 42 via the pipe 421. The fuel is reformed into hydrogen-rich gas in the reformer 41. The hydrogen-rich gas is sent into the fuel cell unit 40 via the pipe 422. Chemical reaction of the hydrogen-rich gas occurs in the fuel cell unit 40 to generate electricity. Residual hydrogen-rich gas and hot air is sent into the mixing unit 43 from the fuel cell unit 40. The residual hydrogen-rich gas is mixed with the hot air and/or more fuel in the mixing unit 43. The mixture is sent into the combustor 44 from the mixing unit 43. The mixture is burned in the combustor 44. Exhaust from the combustion is sent into the heat exchanger 45 from the combustor 44. Fresh air is sent into the heat exchanger 45 from the atmosphere via the fresh air port 451. Heat exchange occurs in the heat exchanger 45. Hot air is sent into the fuel cell unit 40 from the heat exchanger 45 through the hot air port 453. The exhaust is expelled from the heat exchanger 45 through the exhaust port 452.
The conventional fuel cell system can make use of the residual hydrogen-rich gas. However, the efficiency of the heat exchanger 45 is low for including a finned-type convective heat transfer mechanism.
Therefore, the present invention is intended to obviate or at least alleviate the problems encountered in prior art.